I recently edited this question and now the syntax highlighting is gone (actually, I don't remember if it was there to begin with).
Before clicking Save Edits, the highlighting was visible but not after the save.
What did I do wrong?
There have been changes made to the syntax highlighting functionality recently. The question you linked to is not tagged with a language, so it isn't sure what to do. You could add the [objective-c] tag if that is appropriate (seems like it would be but I did just glance at the question) and that should kick-start the syntax highlighter.